Electrophotographic material



United States Patent 3,240,594 ELECTROPHGTOGRAPHIC MATERIAL Paul Maria Cassiers, Mortsel-Antwerp, and Ren Maurice Hart, Wilrijli-Antwerp, Belgium, assignors to Gevaert llhoto-Producten, Mortsel-Antwerp, Belgium, a Belgian company No Drawing. @riginal application Jan. 30, 1961, Ser. No. 85,474. Divided and this application Mar. 20, 1964, Ser. No. 353,569

Claims priority, application Great Britain, Jan. 29, 1960,

3,325/60; Apr. 26, 1960, 14,652/60 1 Claim. (Cl. 961) This application constitutes a division of our copending application Serial No. 85,474, filed January 30, 1961.

The present invention relates to electrophotographic material and electrostatic recording materials consisting of an electroconductive backing and a photoconductive layer which contains an organic polymeric photoconductive substance or which consists of an organic polymeric photoconductive substance.

Electrophotographic materials are already known which consist of a support and a photoconductive layer containing as photoconductor an inorganic substance such as selenium or zinc oxide or an organic substance such as anthracene, benzidine or a certain type of heterocyclic compound.

Electrostatic recording materials are already known comprising a photoconductive layer, such as antimony trisulphide, over-coated with an insulating layer, such as polystyrene.

Eledtrophotographid processes involve the electrical charging in the dark of an electrophotographic plate or sheet comprising a coating of photoconductive insulating or semi-conductive material on a conductive support or on an insulating support provided with a conductive layer, so that the coating carries a fairly uniform positive or negative charge. The plate or sheet is then image-wise exposed whereby the illuminated areas of the surface are discharged and the electrostatic latent image is obtained. This latent image is then rendered visible e.g. by depositing thereon a finely divided electrostatically attractable material such as a powder, yielding a powder image. In the electrostatic recording methods an obtained electrostatic pattern of the light signals can be read by a suitable playback head.

For carrying out the above described electrophotographic process, involving electrically charging in the dark at photoconductive layer and subsequently imagewise exposing the same to light so that the illuminated areas of the layer are discharged, photoconductive layers are required which on the one hand possess a high dark resisitivity so that they can easily accumulate an electric charge, and on the other hand possess a sulficiently high photoconductivity to enable them easily to deliver the accumulated charge on exposure.

It is known that some groups of polymeric substances can retain in the dark a high electric charge for a considerable period of time, but lose this charge on exposure to an electromagnetic radiation of suitable wave-length.

Polymeric photoconductive substances are e.g. described in our corresponding US. patent applications Nos. 11,128, 11,129, now Patent No. 3,155,503, and 11,130, now Patent No. 3,131,060, all filed February 26, 1960.

Now we have found that electrophotographic materials suitable for use in a wide variety of electrophotographic reproduction methods and electrostatic recording methods can also be obtained by using in the manufacture of the photoconductive layer a polymeric substance or substances obtained by reacting at least one halogen containing polymeric substance (the term polymeric substance" here including homoand copolymers) with at least one aromatic or heterocyclic compound and/or a polymeric substance or substances obtained by reacting at least one compound containing at least one reactive halogen atom with at least one polymer containing aromatic or heterocyclic nuclei.

The exact structure of these reaction products is not known. A possible explanation of the mechanism of reactions leading to the formation of similar reaction products has been proposed by Ph. Teyssi and G. Smets, J. Polymer Sci, XX, 351 (1956). Although many facts seem to support the views of the authors, the present invention is not dependent on any particular theory of the reaction(s) involved in the preparation of the materials used.

A representative although not limitative list of polymeric reaction products particularly suitable for use in the manufacture of a photoconductive layer according to the present invention is given below:

Reaction product of polyvinyl chloride and anthracene Reaction product of polyvinyl chloride and fiuorene Reaction product of polyvinyl chloride and naphthalene Reaction product of polyvinyl chloride and toluene Reaction product of polyvinyl chloride and N-methylphenothiazine Reaction product of polyvinyl chloride and carbazole Reaction product of polyvinyl chloride and phenothiazine Reaction product of polyvinyl chloride and N-etnylcarbazole Reaction product of polyvinyl chloride and phenoxathiine Reaction product of polyvinyl chloride and acridine Reaction product of polyvinyl chloride and lophine Reaction product of after-chlorinated polyvinyl chloride and anthracene Reaction product of chlorinated natural rubber and anthracene Reaction product of after-chlorinated polyvinyl chloride and naphthalene Reaction product of chlorinated natural rubber and naphthalene Reaction product of polyvinyl benzylbromide and N-ethylcarbazole Reaction product of poly(p-isoprenylbenzylbromide) with N-ethylcarbazole Reaction product of the copolymer of vinyl chloride and styrene with naphthalene Reaction product of polystyrene with methylenechloride and fiuorene Reaction product of polystyrene with methylenebromide and fiuorene Reaction product of polystyrene with 1,2-dibromoethane and fiuorene Reaction product of polystyrene with chloroacetylchloride and fiuorene Reaction product of polystyrene with chloroacetylchloride and N-ethylcarbazole Reaction product of polystyrene with 9-bromofiuorene Reaction product of polystryene with a chlorine containing carbazole derivative Reaction product of polystyrene with 9-ethyl- 3-chlorocarbonylcarbazole The reaction products listed hereinbefore can be prepared by application of the Friedel-Crafts reaction wherein aluminum chloride serves as the catalyst.

According to a first preferred embodiment of the preparation a halogen substituted homoor coplymer containing reactive halogen atoms such as polyvinyl chloride is reacted with an aromatic or heterocyclic compound in 3 the presence of a Friedel-Crafts catalyst such as aluminum chloride.

According to a second preferred embodiment of the preparation an aromatic or a heterocyclic compound containing a reactive halogen atom is reacted with a polymer or a coploymer containing aromatic or heterocyclic nuclei.

According to a third preferred embodiment of the preparation an organic compound containing two reactive halogen atoms is reacted with an aromatic or a heterocyclic compound and a polymer or a copolymer containing aromatic nuclei.

It is to be noted that the degree of polymerization of the halogenated polymers is not critical and can vary between wide limits. As far as the copolymers are concerned, it is further to be noted that the content of halogenated groups is not critical and can vary between wide limits, taking into account the properties of the compounds used in the preparation of the copolymers and the required electrophotographic and/ or mechanical properties.

The preparation of some polymeric reaction products for use according to the invention, including some of those listed above is described hereinafter by way of example.

PREPARATION 1 1 mol of a polyvinylchloride and 1 mol of an aromatic product such as fiuorene, naphthalene, toluene are brought into 1250 cm. of dichloroethane. Whilst stirring, 1 mol of aluminum chloride is added at once. The reaction is slightly exothermic and the temperature is maintained below 25 C. After stirring at room temperature for 20 h. the reaction mixture is poured into a fourfold excess of methanol. The polymer precipitate formed is purified by washing with methanol. The polymer is further purified by dissolving in a suitable solvent such as benzene, chloroform, tetrahydrofurane, etc., filtering and precipitating again in methanol, ether or hexane. The intrinsic viscosity of the reaction products formed has been measured at 25 C. in tetrahydrofurane and ranges around 0.08 dl./ g. The analysis and viscosity results of some of the synthesized reaction products are given hereinafter by way of example.

Reaction product of polyvinylchloride and fluorene Intrinsic viscosity: 0.13 dl./g. Analysis (calculated): C, 93.76%;

Found: C, 93.28%; H, 6.26%.

Reaction product of polyvinylchloride and naphthalene Intrinsic viscosity: 0.06 dl./ g. Analysis (calculated): C, 93.50%;

Found: C, 92.4%; H, 5.94%; Cl, 0.6%.

Reaction product of polyvinylchloride and toluene- Intrinsic viscosity: 0.10 dl./ g.

Analysis (calculated): C, 91.53%; H,

Found: C, 90.14%; H, 8.25%, Cl, 1.02%.

PREPARATION 2 1 mol of an halogen containing heterocyclic compound, 1 mol of polystyrene and 1 mol of aluminum chloride are reacted in a suitable solvent such as carbontetrachloride or tetrachloroethane. The reaction can also be carried out with 1 mol of polystyrene, 2 moles of a heterocyclic compound and 1 mol of a compound containing two reactive halogen atoms such as methylene chloride, methylene bromide, 1,2-dibromoethane and monochloroacetylchloride. The preferred reaction medium in this case is carbondisulphide. Purification of the resulting polymer proceeds in the same way as described under Preparation 1. A preparation of a particular polymer according to this method is described hereinafter:

A chlorine containing carbazole derivative is prepared by refluxing for 16 h. 25 g. of N-fl-hydroxypropyl-carbazole with 25 cm. of thionylchloride and 50 cm. of

toluene. The reaction product is precipitated in hexane, redissolved in tetrahydrofurane and finally precipitated in water. After filtration, the reaction product is dried under vacuum. Yield: 11.6 g.; chlorine content: 15.1%.

10 g. of the thus obtained chlorine containing carbazole derivative, 4.3 g. of polystyrene and 5.35 g. of aluminum chloride in 200 cm. of carbon tetrachloride are stirred at room temperature for 48 hours. The reaction product is precipitated in methanol, redissolved in tetrahydrofurane and freed from insoluble impurities by centrifuging. The polymer is finally reprecipitated in methanol, filtrated and dried under vacuum. Yield: 10.6 g.

The present invention includes electrophotographic materials comprising a suitable electroconductive backing in intimate surface contact with a photoconductive layer consisting of or containing (e.g. consisting mainly of) at least one of the reaction products as hereinbefore defined.

For the preparation of the electrophotographic material according to the present invention various techniques can be applied when coating the support with a photoconductive layer.

In practice it is preferable for the polymeric substance or substances involved, either alone or together with other additives such as those described more specifically hereinafter first to be dissolved or dispersed in a suitable organic solvent such as for instance benzene, acetone, methylenechloride, dimethylformamide, tetrahydrofurane, chloroform, carbon tetrachloride or in a mixture of two or more of such solvents. The solution or dispersion thus obtained is uniformly spread on a surface of a suitable support, for instance by centrifuging, spraying, brushing or coating, whereafter the layer formed is dried in such a way that a uniform photoconductive layer is formed on the surface of the support.

Photoconductive layers, consisting wholly or mainly of one or more reaction products of one or more halogenated homoor copolymers and one or more aromatic compounds, and/or of one or more reaction products of one or more halogenated monomers and one or more aromatic polymers, firmly adhere to supports to which they are applied.

The thickness of the photoconductive layers is not critical, but is open to choice within a wider range according to requirements in each individual case. Good results are attained with photoconductive layers of a thickness between 1 and 20 preferably between 5 and 10a. Layers which are too thin do not have a suflicient insulating power and layers which are too thick require extensive exposure times.

Photoconductive layers according to the present invention may contain, in addition to one or more halogen containing reaction products, one or more other photoconductive monomeric or polymeric compounds with similar or different photoelectric, mechanical or other physical properties.

The photoconductive layers according to the present invention may contain besides one or more of the polymeric substances according to the present invention still one or more other photoconductive monomeric or polymeric compounds with similar or different photoelectric, mechanical or other physical properties.

In this way, there are prepared several mixtures of one of the polymeric substances, according to this invention, with substances such as those disclosed in our corresponding U.S. patent applications Nos. 11,128, 11,129 and 11,130. In this respect particularly favorable results are attained with layers consisting of 67 to 99% of a reaction product or products according to the present invention and 1 to 33% of one or more of the vinyl polymers or vinyl copolymers referred to in the specification of our U.S. patent application No. 11,130, filed February 26, 1960.

Further, according to the present invention a compound or compounds which cause an increase of the general sensitivity and/or of the sensitivity to electromagnetic rays from a particular part of the spectrum can also be present in the photoconductive layers, and for this purpose sensitizing compounds may be selected irrespective of whether or not they themselves possess photoconductive properties.

Suitable compounds for increasing the general sensitivity and/or the sensitivity to electromagnetic rays from the visible part of the spectrum are e.g. the sensitizing substances described in U.S. co-pending application No. 11,129. These compounds are preferably used in an amount of 0.1 to 5% in respect of the weight of the polymeric photoconductive substances used.

Finally, there can be present in the photoconductive layer other monomeric or polymeric compounds which confer desired properties on the photoconductive layer and/ or on the composition wherefrom this layer is formed. Thus, e.g., plasticizers such as dibutylphthalate, dimethylphthalate, dimethylglycolphthalate, tricresylphosphate, triphenylphosphate, monocresyldiphenyl phosphate, etc. may be added to the polymeric substance or substances used in the photoconductive layer in amounts of to of the reaction product weight.

Other additives, Well known in the art of surface coating, which may be used, include pigments, and agents controlling viscosity, free flow, ageing and thermal stability, oxidation and/ or gloss. In selecting such additives, preference is given to those substances which do not markedly impair the dark resistivity of the photoconductive layer.

An important feature of the reaction products according to the present invention is their ability to improve the sensitivity of the polymeric materials proposed as photoconductors in the U.S. patent application No. 11,129, particularly when incorporated into a photoconductive layer in amounts varying between 0.5 and 5% in respect of the weight of the said polymeric material.

The reaction products according to the invention are preferably employed in the photoconductive layer of electrophotographic materials wherein the said layer is united with or at least held in intimate surface contact with a backing or support in the form of an electrically conductive plate or sheet member or in the form of an insulating plate or sheet with an electrically conductive layer in contact with the photoconductive layer. An electrically conductive member or layer is a plate, sheet or layer the specific resistivity of which is lower than that of the photoconductive layer, i.e., in general lower than 10 ohm/ cm. Conductive materials the specific resistivity of which is lower than 10 ohm/cm. are preferably used.

Suitable backings or supports in the form of an electrically conductive plate or sheet or in the form of an insulating plate or sheet provided with an electrically conductive layer are described in the U.S. patent application No. 11,129.

Electrophotographic materials according to the present invention can be used in any of the different techniques whatever which are based on the exposure and the discharge of an electrostatic charge provided in or on a photoconductive layer.

The electrostatic charging of the photoconductive layer, the exposure, the transfer of the latent image, if any, the development, the transfer of the powder image, if any, the fixation of the powder image can be carried out as described in the U.S. patent application No. 11,129.

The present invention is not limited in regard to the particular way in which the new electrophotographic materials are used, and the method of charging, the exposure technique, the transfer (if any), the developing method, and the fixing method as well as the materials used in these steps can be chosen according to requirements.

Electrophotographic materials according to the present invention can be applied in reproducing techniques using different kinds of radiations, not only electromagnetic radiations as hereinbefore referred to but also nuclear radiations. For this reason, it should be pointed out that although materials according to the invention are mainly intended for application in processes involving an exposure, the term electrophotography wherever appearing in the description and the claims is used broadly, and includes both xerography and xeroradiography.

The present invention includes also electrostatic recording materials.

The following examples illustrate the present invention without limiting, however, the scope thereof.

Example 1 A g/sq. m. paper support coated with a 10 g/sq. m. baryta layer, is coated with a 6% solution of Hostalit CAM (trademark for a terpolymer of vinyl chloride, vinyl acetate and maleic anhydride manufactured by Farbwerke Hoechst A.G., Frankfurt am Main, Hochst) in methylene chloride. The thus formed material is coated with a 10% solution in methylene chloride of the reaction product of polyvinylchloride and anthracene. After complete drying the photoconductive layer obtained is negatively charged with a corona device whereafter it is exposed reflectographically for 6 see. with a watt lamp at a distance of 10 cm. The development of the latent image formed is carried out with a suitable triboelectrical powder. The powder image thus obtained is brought into contact with a thin wax bearing sheet. The wax melts when heated and makes the powder adhere to the sheet. After stripping off the latter a clear, legible and contrasty image is obtained.

Example 2 A 10 g./sq. m. baryta layer is coated on a 90 g./sq. m. paper stock. This layer is coated with a thin rubber layer from a 0.5% aqueous rubber dispersion. Hereupon is coated a 10% solution of the reaction product of polyvinylchloride and phenoxathiine in chloroform. When the material obtained is thoroughly dried it is charged by means of a corona device and exposed for 6 seconds through a diapositive with a 100 watt lamp at a distance of 10 cm. The electrostatic latent image thus obtained is developed by treating it with a suitable developing powder. After fixing the powder image in known way a very contrasty image is obtained.

Example 3 The metal side of an aluminum paper sheet is coated with a layer from the following solution:

10% solution of the reaction product of polyvinyl chloride and fluorene in acetone cm. 50 10% solution of Hostalit CAM (registered trademark) in methylene chloride cm. 50 Rhoda-mine B (C.I. 45,170) mg. 10

The material obtained after quick drying is positively charged with a corona device whereafter it is contactexposed for 60 sec. through a diapositive with a 100 watt lamp at a distance of 10 cm. When using a suitable reversal toner a directly legible image is produced which is fixed in known way by heat. A very contrasty image is obtained.

Example 4 by means of a suitable powder and fixed by heat. contrasty image is obtained.

A very Example solution of the reaction product of polyvinyl chloride and N-ethylcarbazole in dirnethylformarnide cm. 50 10% solution of Hostalit CAM (registered trademark) in methylene chloride cm. 50 Rhodamine B (C.I. 45,170) mg 10 After drying this material for h. at 50 C. it is charged by means of a corona device and contact-exposed for 1 second through a diapositive to a 100 watt lamp at a distance of 10 cm. After development with a suitable developing powder and fixing by heat a very contrasty reproduction of the original is obtained.

Example 6 8 Example 7 A g./sq. in. paper stock is coated with a 10 g./sq. m. baryta layer. On this support the following solution is 'coated:

Polyvinylcarbazole g 4 Methylene chloride cm.

Friedel-Crafts reaction product of poly (4-vinyl-benzylbromide) and N-ethylcarbazole g 025 The layer is charged by means of a corona device and reflectographically exposed for 2 seconds with a printed original to a 100 watt lamp at a distance of 10 cm. The latent electrostatic image formed is treated with a suitable developing powder yielding a contrasty and vigorous image. By transferring the powder image onto a sheet of writing paper in well known way, 21 directly readable copy is obtained which is fixed by heat and which can be stored for an unlimited period of time.

We claim.

An electrophotographic copying process which comprises exposing an electrostatically charged photoconductive insulating layer comprising a polymeric substance obtained by reacting (A) polystyrene and (B) a reactive organic halogen compound selected from the group consisting of 9-bromofiuorene, 9-ethyl-3-chlorocarbonylcarbazole in the presence of a Friedel-Crafts catalyst to a light image whereby the light struck area is discharged and developing said image of electrostatic charges with an electroscopic material.

No references cited.

NORMAN G. TORCHIN, Primary Examiner. 

